What is an LED and how does it work?

A light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode that emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. LEDs are typically small (less than 1 mm2) and integrated optical components may be used to shape the radiation pattern.

Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared light. Infrared LEDs are still frequently used as transmitting elements in remote-control circuits, such as those in remote controls for a wide variety of consumer electronics. The first visible-light LEDs were also of low intensity and limited to red. Modern LEDs are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.

Early LEDs were often used as indicator lamps for electronic devices, replacing small incandescent bulbs. They were soon packaged into numeric readouts in the form of seven-segment displays and were commonly seen in digital clocks. Recent developments have produced LEDs suitable for environmental and task lighting. LEDs have led to new displays and sensors, while their high switching rates are useful in advanced communications technology.

LEDs have many advantages over incandescent light sources, including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, camera flashes, and lighted wallpaper. As of 2017, LED lights home room lighting are as cheap or cheaper than compact fluorescent lamp sources of comparable output. They are also significantly more energy efficient and, arguably, have a lot of environmental concerns linked to their disposal.


How are LED colours created?

The colour is created by the LED itself without the use of gels or filters. The chemical composition of the semiconductor materials within the LED define the colour of the light produced and the light emitted is monochromatic (single wavelength). Red, green, blue, amber, and several white colours can be created. A white LED is actually a blue LED with a special phosphor coating within the LED structure which converts blue light into white light. This is the reason that many LEDs emit a very cold colour of light, typically in the region of 6000ºK.Warmer white LEDs can now be created using an innovative new phosphor coating technology incorporating red and white emitting phosphors. Our standard white colours now include 6000K, 4000K, 3000K and 2700K.


How is an LED installation wired?

This depends on the installation and the products used. Traditional low power LEDs are provided with a constant voltage then a resistor is used to regulate the current to each LED. High power LEDs require a more sophisticated method to regulate the current to each LED. A typical 1.2W LED requires a regulated constant current of 350mA, the LED itself will self-regulate it’s voltage. If a chain of LEDs are used then they must be wired in series, so each LED receives the required 350mA. The 350mA is provided by specialist power supplies often referred to as drivers. Each driver uses different cable types dependent on the type of fitting it is powering, and all can be mounted remotely – distances again vary dependent on the specific type.


What is a typical lumen output and when will it become a more usable light source?

The efficacy of an LED should be considered, not just the Lumen output. Many LED suppliers quote high power LEDs but with very low efficacies. The efficacy is continually increasing with the roadmap to double in output every two years.


What does LOR stand for and what is the value for LED?

LOR, acronym for Light Output Ratio, is the ratio between the luminous flux emitted by the luminaire, measured at operating temperature (To) and the nominal flux of the LED source. It is a fundamental lighting element because it allows the designer to understand the level of performance of the lighting fitting chosen: the higher this percentage, the more performing the fitting is. This value can be easily observed inside our LDT photometric data available on our website and we are going to update all the data sheets in our web catalog reporting the data on nominal flux, the delivered flux and their relationship, that is the LOR.

The quality of LEDs, combined with an innovative and functional design, allows our fittings to waste as little light as possible and to achieve excellent performance concerning the LOR issue: working with LEDs and aiming to high LOR values means less light dispersion, in other words, more light and more energy saving.


What is the average life expectancy of LEDs?

LEDs have a general life expectancy of 50 000 hrs. If you use your lights for 10 hours a day, this should be 13.7 yrs. If this is correct, then LED’s are definitely an investment, even the top of the range bulb would work out to cost 2.55GBP per year. Add that to the saving you would make on energy and you’ve got a very cost effective bulb!


What is the energy / power consumption?

As a guide, using 1 Watt LEDs power consumption is 1.2 Watts per LED. The drivers are around 85% efficient, therefore the power consumption is approximately 1.4 Watts per LED. However when considering an installation it is important to consider the power consumption of the driver in your calculations, as this value will allow for any relevant gear losses etc.


What is CRI?

CRI or color rendering describes how a light source makes the color of an object appear to human eyes and how well subtle variations in color shades are revealed. The Color Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a "given" light source is at rendering color when compared to a "reference" light source.

The higher the CRI, the better the color rendering ability. Light sources with a CRI of 85 to 90 are considered good at color rendering. Light sources with a CRI of 90 or higher are excellent at color rendering and should be used for tasks requiring the most accurate color discrimination.

It is important to note that CRI is independent of color temperature (see discussion of color temperature). Examples: A 2700K ("warm") color temperature incandescent light source has a CRI of 100. One 5000K ("daylight") color temperature fluorescent light source has a CRI of 75 and another with the same color temperature has a CRI of 90.


What is colour temperature?

The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of a color comparable to that of the light source. Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, horticulture, and other fields. In practice, color temperature is meaningful only for light sources that do in fact correspond somewhat closely to the radiation of some black body, i.e., those on a line from reddish/orange via yellow and more or less white to blueish white; it does not make sense to speak of the color temperature of, e.g., a green or a purple light. Color temperature is conventionally expressed in kelvin, using the symbol K, a unit of measure for absolute temperature.

Color temperatures over 5000 K are called "cool colors" (bluish white), while lower color temperatures (2700–3000 K) are called "warm colors" (yellowish white through red).[1] "Warm" in this context is an analogy to radiated heat flux of traditional incandescent lighting rather than temperature. The spectral peak of warm-coloured light is closer to infrared, and most natural warm-coloured light sources emit significant infrared radiation. The fact that "warm" lighting in this sense actually has a "cooler" color temperature often leads to confusion.


Does an LED get hot and do you have to consider the thermal issues?

The hotter an LED gets the shorter it’s life will be. Ledtroniks design products with this in mind to ensure the typical lifetime of it’s products is in excess of 50,000 hours. High output LEDs will get extremely hot if they are not thermally bonded to a heatsink structure. This extreme temperature would cause rapid degradation of the LED. Ledtroniks incorporate the heatsinks into the design of the product housing which ensures the overall fittings and the LEDs keep relatively cool.


What sort of temperature does an LED housing get to?

Although this can vary throughout the Ledtroniks product range, depending on the size of fitting and number of LEDs used, the average is around 60ºC based on an ambient temperature of up to 40ºC.


What is the maximum operating temperature an LED can operate in?

Ledtroniks’s fittings are designed to operate in an ambient temperature of up to 40ºC. The storage temperature of an LED is considerably higher – in the region of 80-90ºC, therefore fittings can be used in Middle East applications for example, providing they are not operating during daylight hours. If there are concerns on a specific installation, we can provide onboard thermal cut-out solutions to protect the fittings from operating in error during these hot hours.


What is colour binning?

LED chips are mass produced in millions and there are inevitably slight differences in the colour appearance and light output. Binning is way of sorting the chips so that all the LEDs from one particular bin look the same and have similar light output.


Does a colour shift occur in the LED over time?

Colour shift occurs with all light sources over time. Typically if any bulb is replaced it will appear a different colour to adjacent bulbs. The colour shift pattern of LEDs is only very slight and is virtually eliminated with correct thermal management of the fittings. Dimming can cause colour shift with conventional light sources (if you dim a filament/ halogen bulb down it appears red). This is not experienced with LEDs due to the special techniques used in LED dimming systems.


Can LEDs be dimmed and to what level?

Yes. Ledtroniks can currently provide LED drivers which can be dimmed using the following methods:

  • DMX (digital addressable dimming) – hi-tech with individual control of each driver; dimmable to 0%.
  • Mains trailing edge dimmable (traditional type dimming) – used with incandescent light sources dimmable to 20%.
  • 0-10V – typically found with fluorescent installations but this allows a low cost and efficient dimming system to be utilised; dimmable to 10% at 0 volts.
  • Self cycle RGB is a simple colour change driver, with remote control options.
  • Dali – excellent control down to 0% – outstanding dimming